Chart A-1 Dwell Fixed Under 10 Degrees

Chart A-1 - Dwell Fixed Under 10~:

Wiring Diagram for Chart A-1 - Dwell Fixed Under 10~:

CHART A-1 - DWELL FIXED UNDER 10~

Test Description:

1. Determines if the problem is Computer Command Control related or engine related. Dwell should start increasing as soon as engine is choked, and go higher as it is choked more, until it goes over 50~. With severe choking, the dwell could move up scale momentarily even if it is not engine related, but it will move right back to a low dwell. If dwell responds, the problem is a lean engine.

1A. Checks for cause of lean condition that resulted in full rich command.

2. Checks for ECM response to input to O2 sensor circuit. The voltmeter is used to put a voltage on the oxygen sensor circuit to simulate a rich condition. Dwell should increase (a lean command) if ECM and harness are good.


3. Checks for normal coolant sensor circuit condition. Voltage on a normalized hot engine should be under 2.5V.


4. This step checks for an open in the ground circuit to ECM Term. "14" and grounded O2 sensor circuit.


Terminal "2" voltage should be under 1.0 volt at idle. A high voltage could be caused by an open in circuit 452. Normally, this would cause Codes 21 and 34 but, won't set them on some engines.